Acid maltase deficiency Health Article

Definition

Acid maltase deficiency, also called Pompe disease, is a non-sex linked recessive genetic disorder that is the most serious of the glycogen storage diseases affecting muscle tissue. It is one of several known congenital (present at birth) muscular diseases (myopathies), as distinct from a muscular dystrophy, which is a family of muscle disorders arising from faulty nutrition. The Dutch pathologist J. C. Pompe first described this genetic disorder in 1932.

Description

Acid maltase deficiency is also known as glycogen storage disease type II (GSD II) because it is characterized by a buildup of glycogen in the muscle cells. Glycogen is the chemical substance muscles use to store sugars and starches for later use. Some of the sugars and starches from the diet that are not immediately put to use are converted into glycogen and then stored in the muscle cells. These stores of glycogen are then broken down into sugars, as the muscles require them. Acid maltase is the chemical substance that regulates the amount of glycogen stored in muscle cells. When too much glycogen begins to accumulate in a muscle cell, acid maltase is released to break down this excess glycogen into products that will be either reabsorbed for later use in other cells or passed out of the body via the digestive system. Individuals affected with acid maltase deficiency have either a complete inability or a severely limited ability to produce acid maltase. Since these individuals cannot produce the amounts of acid maltase required to process excess glycogen in the muscle cells, the muscle cells become overrun with glycogen. This excess glycogen in the muscle cells causes a progressive degeneration of the muscle tissues.

Acid maltase is an enzyme. An enzyme is a chemical that facilitates (catalyzes) the chemical reaction of another chemical or of other chemicals; it is neither a reactant nor a product in the chemical reaction that it catalyzes. As a result, enzymes are not used up in chemical reactions, but rather recycled. One molecule of an enzyme may be used to catalyze the same chemical reaction over and over again several hundreds of thousands of times. All the enzymes necessary for catalyzing the various reactions of human life are produced within the body by genes. Genetic enzyme deficiency disorders, such as acid maltase deficiency, result from only one cause: the affected individual cannot produce enough of the necessary enzyme because the gene designed to make the enzyme is faulty. Enzymes are not used up in chemical reactions, but they do eventually wear out, or accidentally get expelled. Also, as an individual grows, they may require greater quantities of an enzyme. Therefore, most enzyme deficiency disorders will have a time component to them. Individuals with no ability to produce a particular enzyme may show effects of this deficiency at birth or shortly thereafter. Individuals with only a partial ability to produce a particular enzyme may not show the effects of this deficiency until their need for the enzyme, because of growth or maturation, has outpaced their ability to produce it.

The level of ability of individuals with acid maltase deficiency to produce acid maltase, or their ability to sustain existing levels of acid maltase, are the sole determinants of the severity of the observed symptoms in individuals and the age of onset of these symptoms.

Acid maltase deficiency is categorized into three separate types based on the age of onset of symptoms in the affected individual. Type a, or infantile, acid maltase deficiency usually begins to produce observable symptoms in affected individuals between the ages of two and five months. Type b, or childhood, acid maltase deficiency usually begins to produce observable symptoms in affected individuals in early childhood. This type generally progresses much more slowly than infantile acid maltase deficiency. Type c, or adult, acid maltase deficiency generally begins to produce observable symptoms in affected individuals in the third or fourth decades of life. This type progresses even more slowly than childhood acid maltase deficiency.